Short answer
IW371631 is a reference in the IWC Portugieser Chronograph family. A fake IW371631 is a watch built to look like that reference. The copy uses a third-party chronograph movement and a case from a replica factory. A genuine IW371631 uses IWC calibre 69355, a 41 mm steel case and a sapphire display back. List price on a leather strap sits near $8,000. Copies sell for $150 to $600.
What the reference is
The Portugieser Chronograph uses reference numbers in the 3716 block. The 3716 replaced the earlier 3714 generation. The watch has two counters: chronograph minutes at 12 o'clock and running seconds at 6 o'clock. There is no hour counter.
- Case: stainless steel, 41 mm diameter, about 13 mm thick
- Lug width: 20 mm
- Crystal: sapphire, front and back
- Water resistance: 3 bar (30 m)
- Movement: IWC calibre 69355, automatic, column wheel chronograph
- Power reserve: 46 hours
- Frequency: 4 Hz (28,800 vph)
IWC lists several dial and strap versions inside the 3716 block. Which dial IW371631 carries depends on the market and the production year. Check the current listing on iwc.com before you compare a watch to it.
Movement check
Turn the watch over. The 3716 has a display back. The 69355 shows a column wheel, an openworked rotor with the IWC wordmark and striped bridges. Copies use a Seagull ST19, a Valjoux 7750 clone or a modified 7750. A stock 7750 puts running seconds at 9 o'clock. The reference puts running seconds at 6. If the seconds hand sits at 9, the movement does not match the reference.
Pusher feel is a second data point. The 69355 starts and stops with light pressure and a short click. Clones feel spongy or stiff. This check needs two watches side by side. It is not a single-photo test.
Dial check
- Subdials: recessed, with a circular finish and a printed track ring
- Numerals: applied metal, raised above the dial surface
- Hands: leaf shape, polished with beveled edges
- Printing: sharp edges, no ink spread under a loupe
Copies show flat subdials, painted numerals and a heavier font. Some use glued stickers for the numerals instead of applied metal. A 10x loupe makes the difference clear.
Case, back and engraving
Genuine casebacks carry the reference, a serial number and the IWC name. Laser engraving on copies is shallow and the lines are soft. Compare the serial on the caseback with the serial on the warranty card. A match is a baseline, not proof. Replica sellers copy paperwork.
Case finishing: brushed flanks, polished bevels, even transitions. Copies show rounded edges where the brushing meets the polish. Some have a wider gap at the lug joint.
Size and weight
Measure the case with calipers. The reference measures 41 mm across, crown excluded. Copies run 40.5 mm to 42 mm. Weight on a leather strap sits near 85 g to 100 g. A lighter watch points to a thinner case or a smaller movement.
Price floor
A new IW371631 does not sell for $300. A listing at that level is a copy or a scam. Secondhand genuine examples trade below list, but not at replica prices. Ask for the purchase date, the dealer name and the service record.
What is not known
IWC does not publish a counterfeit guide for this reference. Serial ranges by production year are not public. If a seller cites a specific serial range, treat the claim as unverified. For authentication, use an IWC boutique or an authorized IWC service center.